Rock bolts of the above kind are very popular in underground mining sites throughout the world, because their installation is very simple when compared to other types of rock bolts. All that is required to install such a rock bolt is to drill a bore into the rock strata and then to hammer the rock bolt into the bore. In contrast, other forms of rock bolts employ resin or grout to anchor the rock bolt within the bore. In respect of resin anchored bolts, a resin cartridge is usually employed, which is required to be inserted into the bore prior to the bolt being inserted therein. Insertion of the resin cartridge is sometimes very difficult, because typically the tunnel walls extend to a significant height, so that access to bores into which the cartridge is to be inserted is inconvenient. Additionally, the resin which is employed is relatively expensive and has a limited shelf life.
Cement grouted rock bolts are less expensive than resin anchored bolts, but application of the cement is more cumbersome than that of the resin. Cement grouting requires cement mixing equipment, as well as pumping and delivery equipment, to deliver the mixed cement into the bore.
Despite the installation difficulties of resin and cement anchoring, bolts anchored in either manner generally are much more efficient in respect of rock reinforcement or stabilisation, because such bolts have a significantly better bond between the resin or cement and the bore wall, compared to the frictional engagement of a friction rock bolt. Accordingly, it is usually necessary to employ a greater number of friction rock bolts than compared to resin or cement grouted bolts, or alternatively, the friction rock bolts are required to be longer than resin or cement grouted bolts.
There are other drawbacks associated with the use of friction bolts, such as:                relatively poor shear strength;        sensitivity to corrosion; and        limited ability to support a rock plate against a rock face.        
To overcome some of the drawbacks described above, friction bolts are often post grouted after installation. Advantageously, post grouting increases shear strength and protects against corrosion. It is also possible to reinforce a friction rock bolt with a steel bar or cable in addition to post grouting. In an installation of this kind, the bar or cable is pushed inside the tube of the friction rock bolt immediately after the cement grout has been pumped in. While each of the above modifications to the traditional friction rock bolt improves the performance of the bolt, it will be appreciated that they also significantly add to the installation time and expense of the rock bolt. For example, post grouting can be a difficult process, given that typically grout is introduced through a grout hose, the end of which is fed to the leading end of the rock bolt, whereafter the hose is withdrawn through the length of the rock bolt as grout is pumped into the rock bolt. If withdrawal of the hose is made too quickly, voids can form inside the tube. Moreover, if the grout mixture is too thin, then the grout can flow out of the trailing end of the tube and not fill it. Additionally, it is not always apparent to the operator that enough grout has been pumped in to fill the tube because the existing arrangements do not necessarily provide for an indication that the tube has been filled. Operator experience is therefore critical to correct grouting.
It is an object of the present invention to overcome or at least alleviate one or more of the drawbacks associated with prior art friction rock bolt arrangements.